Diesel and gasoline engines emit soot particles, very fine particles of carbon and soluble organics as well as typical harmful engine exhaust gases (i.e., HC, CO and NOx). Regulations have been enacted curbing the amount of soot permitted to be emitted. To meet these challenges, soot filters constructed of ceramic bodies have been used. In preferred embodiments, ceramic bodies that include an internal honeycomb structure and at least partially surrounded by a skin layer have been developed.
Manufacturing of these ceramic bodies has typically been accomplished via an extrusion process, wherein ceramic bodies are manufactured as individual logs of various lengths. It is also known that bonded assemblies of one or more individual logs are possible, for example as seen in U.S. Pat. No. 6,669,751, and incorporated herein by reference. The cutting of these logs into desired segment lengths, at a relatively high production rate and with minimizing defects, has been the focus of on-going development efforts in industry. This is particularly true when the logs are in a softer state, commonly known as “green ware”. Various cutting and grinding techniques and tools have been developed over the years, for example as disclosed in patent documents US 2007/0096370; U.S. Pat. No. 7,452,263; and US 2008/0233345, as well as numerous text books on the subject, such as Ceramic Technology and Processing, William Andrew Publishing/Noyes, King, A. G. (2002). Handbook of Ceramic Grinding and Polishing, Marinescu, I. D., H. K. Tonshoff, et al. (2000), incorporated herein by reference. Each reference teaches a different tool and/or technique to produce logs at a desired segment length. The method of the present invention is not disclosed. For example, some of the processes disclosed by the references may be limited in the amount of scrap (e.g. length) that can be removed in a single process step, which in turn may increase the time required to produce logs at a given desired segment length. In another example, it is suggested that scoring of the exit corner of the cut be completed prior to cutting the log. Also, it is believed that cutting techniques that utilize a single blade, especially as it exits across the end of the work piece, can contribute to the creation of defects.
Defects in the end surfaces of the logs may be defined broadly as an abnormality in the surface. More explicitly, defects may include cracks or chips (typically greater than about 0.5 mm) in the outer skin layer and/or missing, damaged, or deformed honeycomb walls.
What is needed are processes and tools for preparing extruded ceramic body segments, at commercially acceptable rates, to desired segment lengths without a significant number of defects in the end surfaces (e.g. the outer skin layer and/or the honeycomb structure), that allow for greater flexibility as to the amount of scrap (e.g. length) that can be removed in a single process step.